Catalyst for ring expansion metathesis polymerization of cyclic monomers

ABSTRACT

A tetraanionic OCO pincer ligand metal-oxo-alkylidene complex is prepared from a trianionic pincer ligand supported metal-alkylidyne. The metal can be tungsten or other group 5-7 transition metal. The tetraanionic pincer ligand metal-oxo-alkylidene complex, a trianionic OCO pincer ligand metal complex, or a trianionic ONO pincer ligand metal complex can be used to polymerize cycloalkenes. The poly(cycloalkene)s are predominantly cis-alkene macrocyclics.

CROSS-REFERENCE TO A RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 62/220,569, filed Sep. 18, 2015, the disclosure of which is herebyincorporated by reference in its entirety, including all figures, tablesand drawings.

This invention was made with government support under CHE-1265993awarded by the National Science Foundation. The government has certainrights in the invention.

BACKGROUND OF INVENTION

The ring-expansion metathesis polymerization of cycloalkenes hasreceived significant attention. This polymerization is documented, forexample in Bielawski et al., Science 2002, 297, 2041-44. Recently, Veigeet al. U.S. Patent Application Publication No. 2014/0309389 disclosestridentate pincer ligand supported metal complex of a group 5-7transition metals that initiate polymerization of alkynes in high yieldto macrocyclic polyalkynes. Metal complexes that polymerize alkenes toyield cyclic polyalkenes are desirable. Cyclic norbornene-basedmacromonomers were polymerized via REMP using cyclic rutheniumcatalysts, as described by Boydston et al., J. Am. Chem. Soc. 2008, 130,12775-82. However, control over both tacticity and the cis/trans ratiois either not reported or is absent. Hence, effective catalysts for thepreparation of polymers by stereo-controlled ring-expansion metathesispolymerization are desirable.

SUMMARY OF THE INVENTION

An embodiment of the invention is directed toward a tetraanionic pincerligand metal-oxo-alkylidene complex of the structure:

where: Z is independently O or S; R comprises, independently, H, methyl,ethyl, n-propyl, i-propyl, n-butyl, i-butyl t-butyl, or larger alkyl; R′is methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, C₅-C₂₂alkyl, phenyl, naphthyl, or C₁₃-C₂₂ aryl; X is O, N, S, P, or Se; R″,independently, is methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl,t-butyl, C₅-C₂₂, phenyl, naphthyl, C₁₃-C₂₂ aryl, or two R″ is a C₄-C₆alkylene combined with a single X as a heterocycle; n is 1 to 3; and Mis a group 5-7 transition metal. A representative tetraanionic pincerligand metal-oxo-alkylidene complex has the structure:

The tetraanionic pincer ligand metal-oxo-alkylidene complex can beprepared from the reaction of a trianionic OCO pincer ligand supportedmetal-alkylidyne complex with carbon dioxide or carbon disulfide.

In embodiments of the invention, the tetraanionic OCO pincer ligandmetal-oxo-alkylidene complex, a trianionic OCO pincer ligand metalcomplex, or a trianionic ONO pincer ligand metal complex can be combinedwith a plurality of cyclic alkene monomers to yield a plurality ofcyclic poly(alkene).

In an embodiment of the invention the trianionic OCO pincer ligand metalcomplex has the structure:

In another embodiment of the invention, the trianionic ONO pincer ligandmetal complex has the structure:

Cyclic monomers that can be employed are unsubstituted or substitutedcyclopropene, cyclobutene, cyclopentene, cycloheptene, and cyclooctene,norbomene, dicyclopentadiene, norbomene anhydride, diester fromnorbornene anhydride, imide from norbornene anhydride, oxanorbornene,oxanorbornene anhydride, ester of oxanorbornene anhydride, and imide ofoxanorbornene anhydride, or any combination thereof, wherein the esteris from a C₁-C₁₀ alkyl or aryl alcohol, the imides is from C₁-C₁₀ alkylor aryl amine; wherein substituents can be C₁-C₁₀ alkyl, aryl, C₁-C₁₀alkoxy, aryloxy, C₁-C₁₀ carboxylic acid ester, or carboxylic acid amide,optionally substituted one or two times with C₁-C₁₀ alkyl or aryl.

Polymerization by ring expansion metathesis polymerization can result instereorandom or stereoregular cyclic polymers. A stereoregular cyclicpolynorbornene can be formed with repeating units having greater than95% cis content and greater than 95 percent syndiotactic content.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the crystal structures of OCO tungsten complex 2, accordingto an embodiment of the invention, as determined by a single crystalX-ray diffraction experiment.

FIG. 2 shows the crystal structures of OCO tungsten complex 3, accordingto an embodiment of the invention, as determined by a single crystalX-ray diffraction experiment.

FIG. 3 shows a reaction scheme for the stereoregular polymerization ofnorbornene with complex 2, according to an embodiment of the invention.

FIG. 4 shows plots of log molar mass verses elution volume for cyclicpolynorbornene (top curve) prepared using complex 2, according to anembodiment of the invention, and linear polynorbornene prepared by aprior art method.

FIG. 5 shows plots of log intrinsic viscosity verses log molar mass forcyclic polynorbornene (bottom curve) prepared using complex 2, accordingto an embodiment of the invention, and linear polynorbornene prepared bya prior art method.

FIG. 6 shows plots of root mean square radius of gyration vs. molar massfor cyclic polynorbornene (bottom points) prepared using complex 2,according to an embodiment of the invention, and linear polynorborneneprepared by a prior art method.

FIG. 7 shows reaction schemes for the nearly random polymerization ofnorbornene with complex 4, according to an embodiment of the invention,and a linear polymerization of norbornene with complex 5.

FIG. 8 shows reaction schemes for the stereoregular polymerization ofnorbornene with complex 1, according to an embodiment of the invention,and a linear polymerization of norbornene with Grubb's catalyst 6.

FIG. 9 shows a ¹H-¹H COSY NMR of poly(DCMNBD) using 1, according to anembodiment of the invention, as the catalyst in CDCl₃ at 500 MHz,expansion.

FIG. 10A shows a plot of log molecular mass versus elution volume forstereoregular cyclic polynorbornene synthesized by 1 (top curve),according to an embodiment of the invention, and linear polynorbornenesynthesized by 6.

FIG. 10B shows a plot of log molecular mass versus elution volume forstereorandom cyclic polynorbornene synthesized by 4 (top curve),according to an embodiment of the invention, and linear polynorbornenesynthesized by 5.

FIG. 11A shows a plot of intrinsic viscosity verses molar mass forstereoregular cyclic polynorbornene synthesized by 1 (bottom curve),according to an embodiment of the invention, and linear polynorbornenesynthesized by 6.

FIG. 11B shows a plot of log intrinsic viscosity verses log molar massfor stereorandom cyclic polynorbornene synthesized by 4 (bottom curve),according to an embodiment of the invention, and linear polynorbornenesynthesized by 5.

FIG. 12A shows a plot of root mean square radius of gyration vs. molarmass for stereoregular cyclic polynorbornene synthesized by 1 (bottompoints), according to an embodiment of the invention, and linearpolynorbornene synthesized by 6.

FIG. 12B shows a plot of root mean square radius of gyration vs. molarmass for stereorandom cyclic polynorbornene synthesized by 4 (bottompoints), according to an embodiment of the invention, and linearpolynorbornene synthesized by 5.

FIG. 13 is a reaction scheme for the preparation of BMCNBD.

FIG. 14 shows a 500 MHz ¹H NMR spectrum of 2 and 3 as prepared withoutisolation in C₆D₆.

DETAILED DISCLOSURE

An embodiment of the invention is directed to tetraanionic pincer ligandmetal-oxo-alkylidene complexes of the structure:

where: Z is independently O or S; R is, independently, H, methyl, ethyl,n-propyl, i-propyl, n-butyl, i-butyl t-butyl, or larger alkyl, or anyother substituent that does not inhibit formation of the tetraanionicpincer ligand supported metal-alkylidyne complex; R′ is methyl, ethyl,n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, C₅-C₂₂ alkyl, phenyl,naphthyl, or C₁₃-C₂₂ aryl; X, independently, can be O, N, S, P, or Se;R″, independently, is methyl, ethyl, n-propyl, i-propyl, n-butyl,i-butyl, t-butyl, C₅-C₂₂, phenyl, naphthyl, C₁₃-C₂₂ aryl, or two R″ is aC₄-C₆ alkylene combined with a single X as a heterocycle; n is 1 to 3depending on X; and M is a group 5-7 transition metal.

The OCO pincer ligand contains three anionic donor atoms that complexthe metal ion. The tetraanionic pincer ligand metal-oxo-alkylidenecomplex is generated by the addition of carbon dioxide, carbondisulfide, or, effectively, cabonoxidesulfide to a trianionic pincerligand supported metal-alkylidyne complex where the trianionic pincerligand results from a precursor with the structure:

where R groups at carbons 3, 4, 5, 6, 4′, 5′, 6′, 3″, 4″, 5″ and 6″ ofthe 1,1′:3′,1″ terphenyl assembly can be H, or substituted, with analkyl group, such as methyl, ethyl, n-propyl, i-propyl, n-butyl,i-butyl, t-butyl, or larger alkyl group, for example C₅-C₂₀, or anyother substituents that do not compete for the formation of an M≡C bondof a synthetic precursor trianionic pincer ligand supportedmetal-alkylidyne complex. For example, a substituent that can form achelate toward the metal, alone or in combination with one of the OHgroups of the OCO pincer ligand can be included. Among the othersubstituents on the OCO pincer ligand, R may be groups that permit theattachment of the OCO pincer ligand, a precursor trianionic pincerligand supported metal-alkylidyne complex prepared therefrom, or atrianionic pincer ligand metal-oxo-alkylidene complex prepared therefromto a polymer or resin, for example a carboxylic acid, carboxylic ester,amine, thiol, epoxy, haloalkyl, hydroxy, or other reactive group in the4, 5, 5′, 4″, or 5″ positions. Large R groups at carbons 6, 4′, 6′, and6″ of the OCO pincer ligand precursor can oblige the aromatic rings tobe out of plane to a significant degree and inhibit the formation of thedesired precursor trianionic pincer ligand supported metal-alkylidynecomplex, and, generally, are not appropriate for preparation of thetrianionic pincer ligand supported metal-oxo-alkylidene complexes,according to embodiments of the invention.

In an exemplary embodiment of the invention, as shown in Scheme 1,below, a tetraanionic OCO pincer ligand tungsten-oxo-alkylidene complex2 and a dinuclear species 3 are synthesized from a trianionic pincerligand supported tungsten-alkylidyne complex 1 upon reaction with carbondioxide in a 9:2 ratio.

Complex 2 crystallizes preferentially in C₆D₆, resulting in singlecrystals amenable to X-ray diffraction. The tungsten ion in complex 2,as shown in FIG. 1, is square pyramidal (τ=0.12). The oxo group occupiesthe axial position (W1−O4=1.6948(15) Å) and the alkylidene(W1═C21=1.9503(19) Å), a THF ligand, and two aryloxides reside in thebasal plane.

Complex 3 results from complex 2 by the loss of CO and tetrahydrofuran(THF). Upon extensive heating of the reaction mixture, completeconversion of 2 to 3 is possible. Slow evaporation of a concentratedsolution of 3 in a pentane/Et₂O mixture yields single crystals suitablefor X-ray diffraction, as shown in FIG. 2. One of the aryloxides fromthe trianionic OCO³⁻ pincer ligand bridges the two tungsten atoms. Theconversion of 2 to 3 can be suppressed in the reaction mixture by theinclusion of THF in solution.

In an embodiment of the invention, complex 2 is employed as catalyst forring-expansion metathesis polymerization of cycloalkenes. In anembodiment of the invention, complex 3 is employed as catalyst forring-expansion metathesis polymerization of cycloalkenes to generate acyclic polyalkene. In other embodiments of the invention, a trianionicpincer-supported metal alkylidyne, where the metal is a group 5-7transition metal, is employed as a catalyst in a method forring-expansion metathesis polymerization of cycloalkenes. The trianionicpincer ligand precursor has the structure:

where R groups at carbons 3, 4, 5, 6, 4′, 5′, 6′, 3″, 4″, 5″ and 6″ ofthe 1,1′:3′,1″ terphenyl assembly can be H, or substituted, with analkyl group, such as methyl, ethyl, n-propyl, i-propyl, n-butyl,i-butyl, t-butyl, or larger alkyl group, for example C₅-C₂₀, or anyother substituents that do not compete for the formation of an M≡C bondof a synthetic precursor trianionic pincer ligand supportedmetal-alkylidyne complex. The trianionic pincer ligand can be an OCO³⁻pincer ligand, as in 1, or, in an embodiment of the invention, an ONO³⁻pincer ligand. The ONO³⁻ pincer ligand can be of the structure derivedfrom the protonated precursor:

R groups and R′ groups where X is C are independently H, C₁-C₃₀ alkyl,C₂-C₃₀ alkenyl, C₂-C₃₀ alkynyl, C₆-C₁₄ aryl, C₇-C₃₀ arylalkyl, C₈-C₃₀,C₃-C₃₀ polyether, C₃-C₃₀ polyetherester, C₃-C₃₀ polyester, orarylalkenyl, C₈-C₃₀ arylalkynyl, C₁-C₃₀ alkoxy, C₆-C₁₄ aryloxy, C₇-C₃₀arylalkyloxy, C₂-C₃₀ alkenyloxy, C₂-C₃₀ alkynyloxy, C₈-C₃₀arylalkenyloxy, C₈-C₃₀ arylalkynyloxy, C₂-C₃ alkylester, C₅-C₁₅arylester, C₈-C₃₀ alkylarylester, C₃-C₃₀ alkenylester, C₃-C₃₀alkynylesterperfluorinated, partially fluorinated, and/or otherwisesubstituted variations thereof.

According to an embodiment of the invention, cyclic poly(cycloalkene)scan be homopolymers or copolymers of a plurality of cyclic alkenemonomers where the catalyst functions as the initiator of thepolymerization. Cyclic polymers can be prepared from a wide variety ofcycloalkene monomers, including, but not limited to, monocyclic alkenes,such as, but not limited to cyclopropene, cyclobutene, cyclopentene,cycloheptene, and cyclooctene, and substituted variations thereof,bicycloalkenes, such as, but not limited to, norbornene,dicyclopentadiene, norbornene anhydride, esters from norborneneanhydride, imides from norbornene anhydride, oxanorbornene,oxanorbornene anhydride, esters of oxanorbornene anhydride, and imidesof oxanorbornene anhydride. The imides can be imides from alkyl or arylamines, which can be substituted or unsubstituted. Substituents can beC₁-C₁₀ alkyl, aryl, alkoxy, carboxylic acid ester, carboxylic acidamide, where the amide is optionally substituted one or two times withan alkyl or aryl. Cyclic polymers can be prepared that are copolymers oftwo or more monomers. The molecular weight of the cyclic polymers can besmall, equivalent to oligomers of three to ten repeating units, or themolecular weights can be of any size up to tens and hundreds ofthousands in molecular weight. The cyclic poly(cycloalkene)s can be usedas prepared or converted into cyclic poly(cycloalkane)s upon reductionof the double bonds of the cyclic poly(cycloalkene)s polymer. The cyclicpoly(cycloalkene)s can be converted to substituted cyclicpoly(cycloalkane)s by addition reaction at the alkene groups of thecyclic poly(cycloalkene)s, for example the addition of halogens,alcohols, amines, or any other olefin addition reactions. Themacrocyclic polymers can find many applications, such as part of motoroil additives or other lubricants.

Depending on the catalyst employed, the stereochemistry ofpolymerization varies. For example, the cyclic polymer can be atactic inmonomer placement with approximately 61% cis content with catalyst 4 butin excess of 99% cis content and more than 95% syndiotactic when complex1 or complex 2 is employed as the catalytic initiator, according toembodiments of the invention.

In an exemplary polymerization, as shown in FIG. 3, initiating catalyst2 at 1 mol % with norbornene at room temperature yields cis-selectivecyclic polynorbornene (>98% by ¹H NMR spectroscopy) after 7 h. Thereaction was quenched by dropwise addition of the reaction mixture intostirring methanol. The resulting polymer was isolated by filtration anddried under vacuum. Complex 3 when mixed at 1 mol % with NBE at roomtemperature for 7 h yields polynorbornene in only 42% yield, with nocis-selectivity. Table 1, below, lists polymerization results as afunction of the ratio of monomer to catalyst.

A mixture of 2 and 3 maintains the selectivity of 2 when treated withnorbornene, suggesting initiation with catalyst 2 and propagation of themonomer are much faster than initiation by the more hindered complex 3.Evidence for fast propagation relative to initiation comes from a sealedNMR tube polymerization experiment. Combining norbornene and 2 in C₆D₆results in polymer formation but the ¹H NMR spectrum of the reactionmixture exhibits signals attributable to unreacted catalyst 2. Cyclicpolynorbornene produced with catalyst 2 is syndiotactic (>98%), asdetermined by a comparison to ¹³C NMR data of previously reportedsyndiotactic linear polynorbornene.

TABLE 1 Polymerization of norbornene^([a]) by catalyst 2 with differentmonomer/catalyst ratio yield % M_(n) ^([d]) [mon/cat]₀ [monomer]₀ ^([b])(%) cis^([c]) (kDa) M_(w)/M_(n) ^([d])  25:1 0.1 97 97 126 1.24  50:10.1 97 97 197 1.25 100:1 0.1 92 98 248 1.21 200:1 0.1 60 97 578 1.29^([a])The appropriate amount of a 1 mg/mL solution of catalyst dissolvedin toluene is added to 40 mg of norbornene dissolved in toluene andstirred for 7 h at room temperature. ^([b])mol · L⁻¹. ^([c])Determinedby ¹H NMR spectroscopy. ^([d])Determined by size exclusionchromatography.

Size exclusion chromatography (SEC) equipped with multi-angle lightscattering (MALS) and viscosity detectors provide compelling data for acyclic topology for polynorbornene from complex 2. Cyclic polymers havelower intrinsic viscosities and smaller hydrodynamic volumes than theirlinear analogs. Catalyst that produce linear polynorbornene with highcis selectivity (>95%) and syndiotacticity (>95%) are known, and asample was synthesized utilizing Grubbs catalystRu(NHC(Ad)(Mes)(═CH(PhO^(i)Pr))(η²-NO₃) (6).

TABLE 2 M_(n), M_(w)/M_(n), cis-selectivity and tacticity ofcyclic/linear poly(NBE) M_(n) ^([a]) Catalyst (kDa) M_(w)/M_(n)cis^([b]) Tacticity^([c]) 2 (cyclic) 113 1.16 >98 Syndiotactic 6(linear) 114 2.34 >95 Syndiotactic ^([a])Absolute molecular weightsdetermined by SEC-MALS. ^([b])Determined by ¹H NMR spectroscopy.^([c])Determined by ¹³C NMR spectroscopy.

A plot of log of molar mass versus elution volume is shown in FIG. 4,where the cyclic polynorbornene with the same molar mass elutes laterthan their linear counterparts, consistent with their smallerhydrodynamic volume. A Mark-Houwink-Sakurada (MHS) plot (log [η] versuslog M, where [η] is the intrinsic viscosity and M is theviscosity-average molar mass, as indicated in FIG. 5, confirms the lowerintrinsic viscosity of the cyclic polymers relative to the linearpolymers. The experimental ratio [η]_(cyclic)/[η]_(linear) of 0.34 overa range of molecular weights are in good agreement with the theoreticalvalue of 0.4. MHS parameters a of 0.76 and 0.71 for the linear andcyclic samples, respectively, were determined from the slope of the MHSplots. This result indicates that both polymers behave as flexiblerandom coils in solution, meaning the observed differences are caused bydifferent topologies. In addition a plot of mean square radius ofgyration (<R_(g) ²>) versus molar mass, as shown in FIG. 6, obtained forcyclic and linear samples of polynorbornene provides a <R_(g)²>_(cyclic)/<R_(g) ²>_(linear) ratio of 0.4±0.1, which is within theexperimental error of the theoretical value of 0.5.

Tethering an alkylidene to a substitutionally inert ancillary ligand isan effective design for creating catalysts capable of REMP, as withcatalyst 2, according to an embodiment of the invention. Unique to thissystem, CO₂ cleavage across the metal-carbon triple bond of complex 1leads to the tethered alkylidene catalyst 2. Complex 2 is the firstgroup VI alkylidene complex to function as a REMP catalyst. Thiscatalyst produces cyclic polynorbornene with extremely highstereocontrol.

In another embodiment of the invention, complex 4 reacts slowly withnorbornene to give non-stereoselective cyclic polynorbornene, asindicated in FIG. 7. Evidence for a cyclic topology comes fromcomparison of the cyclic polymers produced with initiator 4 versuslinear non-stereoselective polymers produced with the ONO-trianionicpincer alkylidene [CF₃—ONO]W═CH^(t)Bu(O^(t)Bu) 5. Catalyst 4 differsfrom 5, as 4 contains an alkylidyne capable of ynene metathesis, whereas5 contains an alkylidene. Complex 1 rapidly polymerizes norbornene atroom temperature, as shown in FIG. 8. Treating a solution of norbomenein toluene with 1 (0.25 mol %) results in the quantitative formation ofhighly cis (>99%; ¹H NMR) and syndioitactic (>95%; ¹³C NMR) cyclicpolynorbornene within 30 min. Table 3 lists the results ofpolymerizations with initiator 1. Cyclic polynorbornene produced withinitiator 1 is syndiotactic (>98%), as determined by ¹³C NMR.Polymerizing chiral dicarbomenthoxynorbornadiene (DCMNBD) with complex 1confirms the assignment of a syndiotactic cyclic polymer. For DCMNBDwith a cis/isotactic stereochemistry, the olefinic protons areinequivalent, and therefore couple in a ¹H-¹H COSY NMR spectrum;whereas, in a cis/syndiotactic polymer, the olefinic protons are relatedby a C₂ axis and are equivalent, and thus do not couple. Poly(DCMNBD)produced by initiator 1 does not exhibit coupling between the olefinicprotons, indicating the polymer is syndiotactic, as shown in FIG. 9.

TABLE 3 Polymerization of norbornene catalyzed by 1 under variousmonomer to catalyst loadings. Yield^([e]) % M_(n) ^([d]) [cat/mon]₀^([a]) [monomer]₀ ^([b]) (%) cis^([c]) g/mol M_(w)/M_(n) ^([d]) 1:1000.1 80 94 118,000 1.26 1:200 0.1 83 95 79,800 1.22 1:400 0.1 80 9491,500 1.32 1:400 0.05 99 99 425,000 1.45 ^([a])The appropriate amountof a 1 mg/mL solution of catalyst dissolved in toluene is added to 30 mgof norbornene dissolved in toluene and stirred for 30 min at roomtemperature. ^([b])mol · L⁻¹. ^([c])Determined by ¹H NMR^([d])Determined by gel permeation chromatography (GPC) using THF as themobile phase at 35° C. ^([e])Determined gravimetrically.

Linear polynorbornene, as indicated in Table 4, below, with a similarlyhigh cis selectivity (95%) and syndiotacticity (>95%) was synthesizedusing the known ruthenium Grubbs catalyst 6, as shown in FIG. 8. Sizeexclusion chromatography (SEC) equipped with multi-angle lightscattering (MALS) and viscosity detectors provide compelling data for acyclic topology. Cyclic polymers have smaller hydrodynamic radii thantheir equivalent linear analogs. Consequently, cyclic polymers have alonger elution time for a given absolute molecular weight during SEC.The differences in the plot of the log of absolute molecular weightsversus elution volume, as shown in FIG. 10A for cyclic and linearpolymers from 1 and 6, respectively, and FIG. 10B for cyclic and linearpolymers from 4 and 5, respectively, are consistent with linear versuscyclic polymers.

TABLE 4 M_(n), M_(w)/M_(n), cis-selectivity and tacticity of cyclic andlinear polynorbornene. M_(n) % % Catalyst (g/mol)^([a]) Mw/Mn^([a])cis^([b]) syndiotactic^([c]) 1 (cyclic) 125,000 1.22 >99 >95 6 (linear)114,000 2.34 >95 >95 ^([a])Determined by gel permeation chromatography(GPC) using THF as the mobile phase at 35° C. ^([b])Determined by ¹HNMR. ^([c])Confirmed by ¹H-¹H COSY NMR.

A Mark-Houwink-Sakurada (MHS) plot (log [η] versus log M, where [η] isthe intrinsic viscosity and M is the viscosity-average molecular weight,is shown in FIG. 11A for cyclic and linear polymers from 1 and 6,respectively, and FIG. 11B for cyclic and linear polymers from 4 and 5,respectively, and confirms the lower intrinsic viscosity of the cyclicpolymers relative to the linear sample. The Mark-Houwink parameter (a)values of 0.75 for the linear sample and 0.66 for the cyclic samplesuggest that both behave as random coils in solution. The experimentalratio [η]_(cyclic)/[η]_(linear) over a range of molecular weights agreeswith the theoretical value of 0.4. The root mean square radius (RMS) ofthe two samples was measured. The cyclic polymers exhibited smaller<R_(g) ²> values for a wide range of molecular weights as compared tothose of linear samples, and the experimentally determined ratio of

$\frac{\left\langle R_{g}^{2} \right\rangle_{cyclic}}{\left\langle R_{g}^{2} \right\rangle\text{?}} = {0.44 \pm 0.07}$?indicates text missing or illegible when filed

calculated over the range is within reasonable error limits of thetheoretical value of 0.5, as indicated in FIG. 12A for cyclic and linearpolymers from 1 and 6, respectively, and FIG. 12B for cyclic and linearpolymers from 4 and 5, respectively.

Differential Scanning Calorimetry (DSC) analyses of cyclic poly(NBE)synthesized by 1 (B) and linear poly(NBE) synthesized by 6 (A) wereperformed and the results indicate nearly identical glass transitiontemperatures (T_(g)) for the cyclic and linear poly(NBE). The similarthermal properties are the result of the relatively high molecularweights (>100,000 g/mol) of these polymers, which minimizes thepotential end group effects.

In summary, OCO³⁻ pincer ligands as in 1, or an ONO³⁻ pincer ligand aswith 4 can produce cyclic polymers by REMP, but with vastly differentdegrees of stereo-control. Table 5 below summarizes these differences.

TABLE 5 Properties of the polymers used for comparison. M_(n) % Catalyst(g/mol)^([a]) M_(w)/M_(n) ^([a]) cis^([b]) tacticity^([c])  1 (cyclic)125,000 1.22 >99 >99% syndiotactic 6 (linear) 114,000 2.34 >95 >95%syndiotactic  4(cyclic) 327,000 1.14 61 atactic 5 (linear) 227,200 1.5863 atactic ^([a])Determined by gel permeation chromatography (GPC) usingTHF as the mobile phase at 35° C. ^([b])Determined by ¹H NMR.^([c])Confirmed by ¹H-¹H COSY NMR.

METHODS AND MATERIALS

Unless otherwise specified, all manipulations were performed under aninert atmosphere using glove-box techniques. C₆D₆(Cambridge Isotopes)was dried over sodium-benzophenone ketyl, distilled or vacuumtransferred and stored over 4 Å molecular sieves. Norbornene wasrefluxed over sodium, distilled and stored under argon. Thetungsten-alkylidyne [OCO]W(═C^(t)Bu)(THF)₂ 1 was prepared according toVeige et al. US Patent Application Publication No. 2014/0309389. Thetungsten complexes [CF₃—ONO]W≡C^(t)Bu(THF)₂ 4 and[CF₃—ONO]W═CH^(t)Bu(O^(t)Bu) 5 were prepared according to PatentApplication Publication No. 2014/0073800 and the monomer chiraldicarbomenthoxynorbornadiene (DCMNBD) was prepared according to Gonsaleset al., Journal of the American Chemical Society 2016, 138, 4996-99.Linear cis-syndiotactic-polynorbornene (cis-poly(NBE)) was synthesizedusing the commercially available Grubbs catalyst purchased fromSigma-Aldrich (CAS 1352916-84-7) and used as received. Bromination ofpoly(NBE) was carried out according to the method of Hyvl et al.,Macromolecules 2015, 48, 3148-52. ¹H and ¹³C NMR spectra were obtainedon Varian INOVA spectrometer (500 MHz), or a Mercury spectrometer (400MHz and 300 MHz for proton). Chemical shifts, reported in δ (ppm), werereferenced on the solvent, on the TMS scale for ¹H and ¹³C. Elementalanalyses were performed at Complete Analysis Laboratory Inc.,Parsippany, N.J. Size-exclusion chromatography was performed in THF at35° C. and a flow rate of 1.0 mL/min (Agilent isocratic pump, degasser,and autosampler; columns: three PLgel 5 μm MIXED-D mixed bed columns,molecular weight range 200-400,000 g/mol). Detection consisted of aWyatt Optilab rEX refractive index detector operating at 658 nm, a WyattminiDAWN Treos light scattering detector operating at 656 nm, and aWyatt ViscoStar-II viscometer. Absolute molecular weights and molecularweight distributions were calculated using the Wyatt ASTRA software.Electrospray ionization mass spectrometry (ESI-MS) spectra werecollected by direct injection into an Agilent 6120 TOF spectrometer at agas temperature of 350° C. with fragmentation voltage of 120 V. Thesample was prepared in an argon glovebox and transported in Hamiltongastight syringes. Gas chromatography electron ionization massspectrometry (GC/EI-MS) to identify CO was performed using a RestekCorp. Rxi-5MS column (30 m×0.25 mm i.d. and 0.25 μm df). A FinniganTrace GC Ultra chromatograph was employed using split injection mode,with a split flow rate of 30 mL/min and a GC carrier gas flow of 1mL/min, vacuum compensated. Temperature at the injection port was of250° C., MS transfer line was at 225° C., and a temperature program of35° C. Isothermal was utilized. A ThermoFinnigan (San Jose, Calif.)Finnigan Trace DSQ mass spectrometer was used with electron ionization(EI) of 70 eV, and ion source temperature of 250° C.

Synthesis of 2,3-Bis((menthyloxy)carbonyl)norbornadiene (BMCNBD)

Acetylene dicarboxylic acid (1.00 g, 8.77 mmol), (−)-menthol (3.43 g,21.9 mmol, 2.50 equiv), p-toluenesulfonic acid (0.167 mg, 0.877 mmol,0.100 equiv), and toluene (25 mL) were charged in a round-bottomed flaskequipped with a Dean-Stark apparatus. The solution was heated underreflux for 18 h. The solution was cooled to rt, washed with water (20mL×2) and brine (20 mL), dried (Na₂SO₄), filtered, and concentrated, andthe crude material was purified by column chromatography (hexanes:EtOAc40:1, R_(f)=0.2) to give the product dimenthyl acetylenedicarboxylate Aas a white solid (1.72 g, 4.40 mmol, 50%), as indicated in FIG. 13.

Freshly prepared cyclopentadiene (0.42 mL, 5.1 mmol, 2.0 equiv) wasadded to a stirred solution of A (1.00 g, 2.56 mmol) in DCM (4 mL) atrt. After 14 h the solution was concentrated, and the crude material waspurified by column chromatography (hexanes:EtOAc 20:1, R_(f)=0.3) andrecrystallization (MeOH) to give BMCNBD as a white solid (935 mg, 2.04mmol, 80%).

Synthesis of [OC^(CO)O]W(O)(THF) 2 and Dimer 3

A J-Young NMR tube was charged with tungsten alkylidyne[OCO]W≡CC(CH₃)₃(THF)₂ (1) (0.050 g, 0.065 mmol) in C₆D₆. Afterperforming a freeze-pump-thaw procedure to evacuate the headspace of thetube, 1 atm of CO₂ was admitted into it. Heating up the reaction up to55° C. for 12 h generates the tungsten oxo alkylidene 2, along withcomplex 3 in a 9:2 ratio, respectively, and as indicated in the protonNMR spectrum shown in FIG. 14. The solvent was evaporated under reducedpressure yielding a red powder. 2 ¹H NMR (C₆D₆, 500 MHz) δ (ppm): δ 7.32(d, 2H, Ar—H), 7.27 (m, 2H, Ar—H), 6.94 (d, 1H, Ar—H), 6.88 (m, 2H,Ar—H), 6.83 (m, 2H, Ar—H), 1.65 (s, 18H), 1.28 (s, 9H). ¹³C determinedby ¹H-¹³C gHSQC and gHMBC experiments: (C₆D₆): δ=273.4 (s, W═Cα), 185.81(s, W≡CCO), 168.0 (s, Ar C), 144.5 (s, Ar C), 137.5 (s, Ar C), 134.9 (s,Ar C), 131.7 (s, Ar C), 130.0 (s, Ar C), 127.5 (s, Ar C), 126.6 (s, ArC), 121.7 (s, Ar C), 121.3 (s, Ar C), 41.7 (s, W═CC(CH₃)₃), 34.8 (s,Ar—C(CH₃)₃), 31.7 (s, W═CC(CH₃)₃), 30.4 (s, Ar—C(CH₃)₃). Red crystalsfrom complex 2 were obtained from a C₆D₆ solution of the reactionmixture, washed with pentane and dried. Asymmetric unit contains onemolecule of benzene. Yield (0.020 g, >41%) Elemental analysis calcd. (%)for C₄₂H₅₀O₅W (818.70 g/mol): C, 61.62; H, 6.16; Found: C, 61.21, H,5.93. HRMS (ESI-MS) m/z: [M+H]⁺ Calcd for C₃₆H₄₅WO₅ ⁺ 741.2771; Found741.2754. The remaining mixture of 2 and 3 was then heated up for 10days at 70° C. to provide complex 3 in quantitative yield. 3 ¹H NMR(C₆D₆, 500 MHz) δ (ppm): δ 7.39 (d, 2H, Ar—H), 7.33 (d, 2H, Ar—H), 7.26(m, 2H, Ar—H), 7.17 (m, 1H, Ar—H), 6.86 (m, 211, Ar—H), 1.71 (s, 18H),0.90 (s, 9H). ¹³C determined by ¹H-¹³C gHSQC and gHMBC experiments:(C₆D₆): δ=280.9 (s, W=Cα), 168.7 (s, Ar C), 147.6 (s, Ar C), 138.8 (s,Ar C), 131.8 (s, Ar C), 131.0 (s, Ar C), 129.1 (s, Ar C), 128.6 (s, ArC), 126.5 (s, Ar C), 124.8 (s, Ar C), 119.6 (s, Ar C), 45.1 (s,W═CC(CH₃)₃), 35.1 (s, Ar—C(CH₃)₃), 33.3 (s, W═CC(CH₃)₃), 30.4 (s,Ar—C(CH₃)₃). HRMS (ESI-MS) m/z: [M+H]⁺ Calcd for C₆₂H₇₃W₂O₆ ⁺ 1281.4435;Found 1281.4415; m/z [M+2H]²⁺ Calcd for C₂H₇₄W₂O₆ ²⁺ 641.2257: Found641.2251.

Polymerization of Norbornene Using Complex 2

To a 20 mL glass vial charged with norbornene (0.038 g, 4.1×10⁻⁴ mol,100 equiv.) in 1 mL of toluene were added 3 mL of a 1 mg/mL solution of2 in toluene (3 mg, 4.1×10⁻⁶ mol, 1 equiv.). The reaction was allowed tostir for 7 h at room temperature. After this period the reaction vesselwas brought outside the glovebox and the reaction mixture was addeddropwise to stirring methanol. Polynorbornene precipitates out and isisolated by filtration, and dried overnight under vacuum. Yield (0.035g, 92%). ¹H and ¹³C NMR spectral assignments were consistent withliterature reports.

Tacticity of the polynorbornene is consistent with the results of thepost-functionalization of polynorbornene via bromination, as recentlydescribed by Schrock and coworkers. The brominated polymer exhibits twodoublets at 3.84 ppm (J=11.2 Hz) and 3.81 ppm (J=10.3 Hz). Consistentwith reported cis, syndiotactic polynorbornene, irradiating the methineprotons at 2.61 ppm results in two singlets. Further evidence for highsyndiotacticity comes from polymerization of the chiral monomer,bis((menthyloxy)carbonyl)norbornadiene (BMCNBD). COSY NMR is able todistinguish between isotactic and syndiotactic poly(BMCNBD). In the caseof a cis isotactic sample, the olefinic protons are inequivalent, andtherefore couple in a COSY NMR spectrum. However, a cis syndiotacticpoly(BMCNBD) contains equivalent olefinic protons related by a C₂ axis,and thus do not couple. Poly(BMCNBD) produced by 2 does not exhibit anycoupling between the olefinic protons, indicating the polymer issyndiotactic.

Polymerization of Norbornene Using Complex 3

To a 20 mL glass vial charged with norbornene (0.019 g, 2.0×10⁻⁴ mol,100 equiv.) in 1 mL of toluene was added 3 (2.6 mg, 2.0×10⁻⁴ mol, 1equiv.) in 1 mL of toluene. The reaction was allowed to stir for 7 h atroom temperature. After this period the reaction vessel was broughtoutside the glovebox and the reaction mixture was added dropwise tostirring methanol. Polynorbonene precipitates out and is isolated byfiltration, and dried overnight under vacuum. Yield (0.008 g, 42%). Amixture of cis and tram polynorbornene was obtained. Tacticity was notdetermined.

Polymerization of Norbornene Using Grubb's Catalyst (6)

A solution of norbornene (0.580 g, 6.16×10⁻³ mol, 1000 equiv.) in 30 mLof THF was added to a 100 mL round bottom flask containing a stirringbar. This solution was cooled to −40° C. and 50 μl, of a stock solution(0.039 g in 0.5 mL of THF) of complex 6 (6.15×10⁶ mol, 1 equiv.) wereadded to it. The reaction was allowed to stir for 1 h at −40° C. Afterthis period 0.1 mL of ethyl vinyl ether was used to quench the reaction,which was then added dropwise to stirring methanol. Polynorborneneprecipitates out and is isolated by filtration, and dried under vacuum.Yield (0.221 g, 38%). ¹H and ¹³C NMR spectral assignments wereconsistent with literature reports.

Polymerization of Norbornene by Catalyst 4

In a nitrogen filled glovebox, norbornene (32 mg, 3.4×10⁻⁴ mol, 12equiv) was dissolved in 1 ml of C₆D₆ and transferred to a scaled NMRtube. In another vial 4 (26 mg, 2.8×10⁻⁵ mol, 1.0 equiv) was dissolvedin 1 mL of C₆D₆ and is added to the NMR tube. After 5 h the mixture wasdissolved in a small amount of toluene (3 mL) and was added dropwise tostirring methanol. The mixture was allowed to stir for 30 min.Polynorbonene precipitates as a white solid and was isolated byfiltration, and dried overnight under vacuum. (28 mg, 88%). ¹H and ¹³CNMR spectral assignments were consistent with literature reports.

Polymerization of Norbornene by Catalyst 1

In a nitrogen filled glovebox, a 20 mL glass vial was charged withnorbornene (30.0 mg, 3.19×10⁻⁴ mol, 400 equiv) and dissolved in 5.76 mLof toluene. To the first solution a 1.0 mg/L solution of 1 (0.61 mL,7.94×10⁻⁷ mol, 1.0 equiv) was added. The reaction was stirred for 30 minat room temperature. After this period the reaction vessel was broughtoutside the glovebox and the reaction mixture was added dropwise tostirring methanol. The mixture was allowed to stir for 30 minutes.Polynorbornene precipitated as a white solid and was isolated byfiltration and dried overnight under vacuum. Yield (29 mg, 97%). ¹H and¹³C NMR spectral assignments were consistent with literature reports.Other polymerization results are tabulated in Table 5, below.

TABLE 5 Polymerization of norbornene by catalyst 1 with differentmonomer/catalyst ratio and monomer concentration. Yield^([e]) % M_(n)^([d]) [cat/mon]₀ ^([a]) [monomer]₀ ^([b]) (%) cis^([c]) (g/mol)M_(w)/M_(n) ^([d]) 1:100 0.1 80 94 118,000 1.26 1:200 0.1 83 95 79,8001.22 1:400 0.1 80 94 91,500 1.32 1:400 0.05 99 99 425,000 1.45 ^([a])Theappropriate amount of a 1 mg/mL solution of catalyst dissolved intoluene is added to 30 mg of norbornene dissolved in toluene and stirredfor 30 min at room temperature. ^([b])mol · L⁻¹. ^([c])Determined by ¹HNMR ^([d])Determined by gel permeation chromatography (GPC) using THF asthe mobile phase at 35° C. ^([e])Determined gravimetrically.

Polymerization of Norbornene by Catalyst 5

In a nitrogen filled glovebox, norbornene (35 mg, 3.7×10 mol, 15 equiv)was dissolved in 1 ml of C₆D₆ and transferred to a sealable NMR tube. Inanother vial, 5 (21 mg, 2.5×10⁻⁵ mol, 1.0 equiv.) was dissolved in 1 mLof C₆D₆ and was added to the NMR tube. After 5 h the mixture wasdissolved in a small amount of toluene (3 mL) and added dropwise to astirring methanol solution. The polymer was then recovered by filtration(30 mg, 86%). ¹H and ¹³C NMR spectral assignments were consistent withliterature reports.

All patent applications, and publications referred to or cited hereinare incorporated by reference in their entirety, including all figuresand tables, to the extent they are not inconsistent with the explicitteachings of this specification.

It should be understood that the examples and embodiments describedherein are for illustrative purposes only and that various modificationsor changes in light thereof will be suggested to persons skilled in theart and are to be included within the spirit and purview of thisapplication.

1. A tetraanionic pincer ligand metal-oxo-alkylidnene complex of thestructure:

where: Z is independently O or S; R comprises, independently, H, methyl,ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, or larger alkyl;R′ is methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl,C₅-C₂₂ alkyl, phenyl, naphthyl, or C₁₃-C₂₂ aryl; X is O, N, S, P, or Se;R″, independently, is methyl, ethyl, n-propyl, i-propyl, n-butyl,i-butyl, t-butyl, C₅-C₂₂, phenyl, naphthyl, C₁₃-C₂₂ aryl; or two R″ is aC₄-C₆ alkylene combined with a single X as a heterocycle; n is 1 to 3;and M is a group 5-7 transition metal.
 2. The tetraanionic pincer ligandmetal-oxo-alkylidene complex according to claim 1, wherein the structureis:


3. A method to prepare a tetraanionic pincer ligand metal-oxo-alkylidenecomplex according to claim 1, comprising: providing a trianionic pincerligand supported metal-alkylidyne complex; combining the trianionicpincer ligand supported metal-alkylidyne complex with carbon dioxide,carbon disulfide, or a mixture thereof; and optionally, warming themixture of trianionic pincer ligand metal-alkylidyne complex with carbondioxide, wherein a tetraanionic pincer ligand metal-oxo-alkylidenecomplex is formed.
 4. A method of polymerizing a cyclic alkene,comprising providing a catalytic initiator selected from a tetraanionicOCO pincer ligand metal-oxo-alkylidene complex, a trianionic OCO pincerligand metal complex, or a trianionic ONO pincer ligand metal complex;providing a plurality of cyclic alkene monomers; and combining thecatalytic initiator with the cyclic alkene monomers, polymerizing theplurality of cyclic alkene monomers into a macrocyclic poly(alkene). 5.The method of claim 4, wherein the tetraanionic OCO pincer ligandmetal-oxo-alkylidene complex has the structure:


6. The method of claim 4, wherein the trianionic OCO pincer ligand metalcomplex has the structure:


7. The method of claim 4, wherein the trianionic ONO pincer ligand metalcomplex has the structure:


8. The method of claim 4, wherein the cyclic monomer is unsubstituted orsubstituted cyclopropene, cyclobutene, cyclopentene, cycloheptene, andcyclooctene, norbomene, dicyclopentadiene, norbomene anhydride, diesterfrom norbomene anhydride, imide from norbomene anhydride, oxanorbornene,oxanorbornene anhydride, ester of oxanorbornene anhydride, and imide ofoxanorbornene anhydride, or any combination thereof, wherein the esteris from a C1-C10 alkyl or aryl alcohol, the imides is from C1-C10 alkylor aryl amine; wherein substituents can be C1-C10 alkyl, aryl, C1-C10alkoxy, aryloxy, C1-C10 carboxylic acid ester, or carboxylic acid amide,optionally substituted one or two times with C1-C10 alkyl or aryl.
 9. Astereoregular cyclic polynorbornene, consisting of repeating unitshaving greater than 95% cis content and greater than 95 syndiotacticcontent.
 10. The stereoregular cyclic polynorbornene according to claim9, wherein the degree of polymerization is 3 to 100,000.
 11. The methodof claim 4, further comprising the step of reducing the double bonds ofthe macrocyclic poly(alkene), thereby forming a macrocyclicpoly(alkane).
 12. A stereoregular cyclic poly(cycloalkane) consisting ofrepeating units having greater than 95% syndiotactic content.
 13. Themethod of claim 4, wherein the tetraanionic OCO pincer ligandmetal-oxo-alkylidene complex has the structure:


14. The method of claim 4, wherein the tetraanionic OCO pincer ligandmetal-oxo-alkylidene complex has the structure:


15. The method of claim 4, wherein the tetraanionic OCO pincer ligandmetal-oxo-alkylidene complex has the structure: